Device for providing an indication of the distance travelled by an object under conditions of acceleration

ABSTRACT

A device for providing an indication of the distance travelled by an object under conditions of acceleration comprising an elongated plate-like member which is longitudinally displaceable, under set back forces, in a direction opposite to that of said acceleration and with respect to a frame-like member fixed with respect to the object, spring biasing means for resisting the longitudinal displacement of said plate-like member and an abutment system associated with said members such that longitudinal displacement of the plate-like member is accompanied by a reciprocating, transverse displacement of the plate-like member.

United States Patent [1 1 Popper et al.

[ 1 3,744,424 1 July 10, 1973 DEVICE FOR PROVIDING AN INDICATION OF THEDISTANCE TRAVELLED BY AN OBJECT UNDER CONDITIONS OF ACCELERATION [75]Inventors: Jakhin Boaz Popper, Kiryat Motzkin; Raphael Cohen, Haifa,both of Israel [73] Assignee: The State 01 Israel, Ministry of Defense,Hakirya Tel Aviv, Israel 22 Filed: Aug. 5, 1970 [21] Aprpl. No.2 61,059

[52] US. Cl. 102/78, 73/511, 102/76 P [51] Int. Cl. F42c 15/24 [58]Field of Search 102/78, 79, 80, 82,

[56] References Cited UNITED STATES PATENTS 9/1960 Hunt, Jr. et al102/78 10/1971 Burke 102/79 2,475,730 7/1949 Wandrey.... 102/78 X2,537,953 1/1951 Andrews.... 102/78 3,151,558 10/1964 Lunati 102/78Primary ExaminerSamuel W. Engle Attorney-Browdy & Neimark [57] ABSTRACT8 Claims, 7 Drawing Figures PAIENIE JUL 1 0191-3 SHEET 2 [1F 3 2 W F wflmm w h "d L. u T m f .u 4 4 lna 32:.

PATENIEDJUL 1 0 ma sum 3 OF 3 FIG. 5b

FIG. 5a

DEVICE FOR EROVEDING AN INDICATION OF THE DISTANCE TRAVELLED BY ANOBJECT UNDER CONDITIONS OF ACCELERATION This invention relates to adevice for providing an indication of the distance travelled by anobject under conditions of acceleration, which term includes bothpositive and negative acceleration of a magnitude which exceeds that ofg. The invention relates particularly to the use of such a device in thearming mechanism of a detonator fuse for a shell or like projectile.

The function of an arming device is to change the condition of a fusefrom a safe condition to a state of readiness for functioning, i.e. fordetonation. The latter takes place only after arming, whether in the airor on impact. Arming on the other hand is initiated with the projectileinside the launching weapon but safety conditions dictate that armingshould under no circumstances be completed before the fuse (to be armed)has left the weapon.

The arming process with which the present invention is particularlyconcerned is one which is initiated when the fuse receives a triggeringaction, such as that obtained when the projectile is fired. The timeinterval during which the fuse changes from an unarmed to an armedcondition is referred to as the arming delay. Among arming devices whichhave been proposed for this purpose are those which are designed tooperate under the so-called set back forces which are developed as aresult of the high acceleration of the projectile upon firing. Witharming devices of this type, however, a problem arises in view of thefact that the firing conditions which give rise to the set back forcesand which lead, after the arming delay, to the arming of the fuse can besimulated by extraneous circumstances, i.e. circumstances other thanthose of firing and thereby lead to an undesired arming of the fuse.Such circumstances include any wherein the projectile is subjected tohigh acceleration, e.g. as a result of a sudden impact or fall. Aproperly designed arming device of this type must be such that whilst itis capable of actuation under genuine firing conditions it will not beactuated as a result of such extraneous circumstances.

Any attempt to meet this requirement by ensuring that the device onlyresponds to accelerations greater than a certain minimum value is notpracticable seeing that in many cases the accelerations induced throughfiring can be quite low and of the same order as or even less than thoseinduced by the extraneous circumstances referred to above and, obviouslythe arming device must be effective to ensure arming as a result of theoperation of set back forces arising from such relatively lowaccelerations.

The present invention proposes to overcome this difficulty by utilizing,as the determining factor in the o'peration of the arming device, notthe absolute magnitude of the acceleration which is developed but ratherthe integrated value of the acceleration over the time during which itis effective, i.e. the distance travelled by the projectile providedwith the arming device when under conditions of acceleration above acertain minimum. Thus, with a device designed to operate on this I basisit can be ensured that the arming delay involved It is an object of thepresent invention to provide a new, improved and simple device forproviding an indication of the distance travelled by an object underconditions of acceleration and wherein due account has been taken of theconsiderations referred to above.

According to the present invention there is provided a device forproviding an indication of the distance travelled by an object underconditions of acceleration comprising an elongated plate-like memberwhich is longitudinally displaceable, under set back forces, in adirection opposite to that of said acceleration and with respect to aframe-like member fixed with respect to the object, spring biasing meansfor resisting the longi tudinal displacement of said plate-like memberand an abutment system associated with said members such thatlongitudinal displacement of the plate-like member is accompanied by areciprocating, transverse displacement of the plate-like member.

It can be shown that with a device in accordance with the invention therestraining forces acting on the plate and inhibiting its longitudinaldisplacement under the set back forces are proportional to the square ofthe speed of the object. This fact can be shown to be particularlyfavourable when the device is incorporated in an arming device for ashell fuse or the like and it ensures that whilst the fuse becomes armedas a result of firing the shell and after leaving the launching weapon(within a wide range of firing accelerations) the dangers of accidentalarming as a result of impact, fall or like extraneous circumstances areminimal. It will be understood, however, that the spring biasing meansis designed to exert a restoring force on the plate which is less thanthe minimum set back forces which are exerted on the plate during firingacceleration thus restoring force ensuring that accelerations less thana certain minimum value will not be effective in initiating thedisplacement of the plate.

In accordance with a specific aspect of the present invention there isprovided a set back arming device for use in a shell fuse or the likeand including an elongated plate-like member which is longitudinallydisplaceable, under set back forces in a direction opposite to thedirection of acceleration of the shell and with respect to a frame-likemember fixed with respect to the fuse, spring biasing means for exertinga restoring force on said plate-like member less than the minimum setback forces exerted on the plate during firing, an abutment systemassociated with said members such that longitudinal displacement of theplate-like member is accompanied by a reciprocating transversedisplacement thereof and retaining means for retaining said plate-likemember in its displaced position when said displacement reaches apredetermined value.

With such an arming device the set back forces generated as a result offiring are such as to ensure the displacement of the plate-like memberagainst the spring restoring force by said pre-determined valuewhereupon the plate-like member is retained in this position against areturn displacement under the influence of the spring restoring forceonce acceleration has ceased. in this way the fuse becomes armed. Where,however, the set back forces are generated as a result of impact orother extraneous circumstances and are sufficiently strong to overcomethe spring biasing force and cause displacement of the plate-like memberthe integrated value of the acceleration as represented by thedisplacement of the plate-like member is not sufficient to displace thelatter by the predetermined value and thereby to cause retention of theplate-like member and therefore as soon as the acceleration ceases theplate-like member is restored by the spring biasing means to itsoriginal position and thus arming does not occur.

In accordance with a preferred embodiment of said invention saidabutment system comprises a pair of parallel elongated serrated edgesformed on one of said members and a pair of abutments carried by theother of said members and respectively and altematingly adapted to abutsaid edges.

For a better understanding of the present invention and to show how thesame may be carried out in practice reference will now be made to theaccompanying drawings in which:

FIG. I is a partially sectioned front elevation of a shell fuseincluding a set back arming device in accordance with the invention,

FIG. 2 is a longitudinally sectioned view of the shell shown in FIG. 1taken along the line IIII,

FIG. 3 is an exploded view (partially sectioned) of the arming deviceshown in FIGS. 1 and 2,

FIGS. 4a and 1b are views of the arming device shown in FIGS. 1, 2 and 3represented schematically before and after arming respectively, and

FIGS. a and 5b are respective schematic representations of an armingplate designed to illustrate limiting locking conditions.

As seen in FIGS. 1 and 2 of the drawings the bomb fuse comprises acasing having a conical nose portion 1 and a substantially cylindricalbody portion 2, a screw threaded portion 3 being formed at anintermediate position on the body portion 2 so as to enable the fuse tobe screwed into the body of a shell (not shown).

Fitting inside the casing wall 4 of the cylindrical body portion 2 is atwo piece slider housing 5a and 5b (see FIG. 3) which are super-imposedand are coupled together by appropriately inter-engaging projections andrecesses (not shown). The housing parts 5a and 5b define between them anelongated transverse pathway 6 in which is slidable an elongatedmetallic slider 7.

The housing portion 5a has formed therein a central longitudinallydirected striker pin aperture in which is slidable a striker pin 9whilst aligned therewith in the lower housing portion 5b is a lead tube10 accommodating a lead detonator 11 l, the base of the housing portion5b is fitted with a disc 112 whose portion opposite the lead detonator111 is apertured, the region between the disc 12 and the base of thecylindrical body portion of the fuse 2 being filled with a booster I13.

Formed in the slider 7 is a blind ended recess 14 which, in the unarmedposition on the fuse is shown aligned with the striker pin 9. To theleft of the blind recess I4 is a throughgoing aperture 15 filled with adetonator H6. The left-hand end of the slider is formed with alongitudinal recess 17 in which is located a compression spring 11$which bears at the right hand end on the base of the recess formed inthe slider and on the left hand end of the neck of a cylindrical stud119 formed integrally with the body casing 41 and projecting into therecess 117.

Adjoining the lead tube 2 and parallel thereto in the housing portion 5bis a tubular bore 20 in which is located a compression spring 211 whoselower end bears against the disc I2 and whose upper end surrounds thestem of a pressure stud 22.

The head of the pressure stud 22 is pressed against an outwardlyextending tongue 23 of an arming plate 24 which, as seen in FIG. ll ofthe drawings abuts the right hand end of the slider 7. As can be seenclearly in FIG. 2 of the drawings the arming plate 24 consists of anupper wide portion 25 which tapers uniformly to an elongatedsubstantially rectangular portion 26, the longitudinal edges 26a and 26bof which are serrated, the crest of each serration of the edge 26 beinglaterally aligned with the recess of each serration on the edge 26b.

As indicated before the tongue 23 is stamped out of the plate 24 so asto extend normally therefrom whilst at the lower end of the plate 24 asecond and smaller tongue 27 is stamped out of the plate 24 so as toextend normally therefrom in a direction opposite to that of the tongue23.

As seen in FlG. I1 and 3 of the drawings, in the unarmed state of thefuse the upper portion of the plate including the wider element 25thereof is located in a longitudinally directed slot 2ft formed in theupper slider housing portion 5a, the central portion of the plate islocated adjacent the right hand end of the slider 7 and prevents thedisplacement of the slider 7 to the right in the slider pathway underthe influence of the compression spring lit The lower portion of theplate is located in an enlarged, longitudinally directed slot 29, formedin the lower slider housing portion 5b adjacent the elongated aperture211) and communicating therewith via a longitudinally directed slit 30through which the tongue 23 projects and is slidable. As can be seenclearly in FllGS. l and 3 of the drawings the width of the slot 2% isgreater than that of the plate 243 and in consequence, as a result ofthe turning moment exerted on the tongue 23 by the spring biasedpressure stud 22, the plate 24 tends to pivot in a clockwise directionadopting the slightly inclined position shown in FIG. 11. At the sametime the outer edge of the lower tongue 27 bears against thelongitudinal wall of the recess 29 formed in the slider houser portionSb.

Projecting downwardly from the slider housing portion 5a into anappropriate recess formed in the upper surface of the slider houserportion 5b, said recess merging into the elongated bore 29, are a pairof retaining legs Bil.

Projecting transversely out of the slider 'houser 5b into the elongatedrecess 29 are a pair of abutment pins 32a and 32b, these pins beinglocated adjacent the edges 26a and 26b of the plate 24 and in a widenedportion 29a of the recess 29 said widened portion narrowing into areally relatively narrow portion 29b thereof.

In operation and with the arming plate 24 shown in the unarmed positionas seen in FIGS. ll, 2 and 41a of the drawings, the fuse is unarmed andif for any reason the striking pin 9 is displaced downwardly it merelyenters the blind recess 114i seeing that the stab initiated detonator116 is displaced therefrom. When now the fuse as a whole is subjected toacceleration for whatever reason and the acceleration is such that theset back forces induced in the plate 24 are greater than the restoringforce of the spring 211 these set back forces will result in thedisplacement of the plate 24 in a direction opposite to the direction ofthe acceleration and against the restoring force of the spring 2ll. Thedisplacement, however, of the plate 24 in its longitudinal direction isalso accompanied by a reciprocating displacement in a transversedirection as a result of the successive abutdegree of displacement ofthe plate gives a measure of 5 the the path length during which the fuseis subject to acceleration.

The design of the device is such that when the acceleration is of thekind induced by the firing of the shell this acceleration is of asufficient magnitude and persists for a sufficient length of time forthe plate to be displaced downwardly over substantially its full lengthuntil the lower end of the stem of the pressure stud 22 abuts againstthe disc 12 whereupon the turning moment imparted to the plate 24 pivotsit underneath the retaining legs 31 thereby locking the plate inposition and preventing its return movement under the influence of therestoring spring even though the acceleration may have ceased (see FIG.4b). Under these circumstances the fuse can be considered to be armedand the slider 7 can move to the right after (if necessary) apredetermined delay which is now initiated. With the completion of thisdelay the detonator 16, the striker pin 9 and the lead detonator 11 arealigned and upon detonation the striker pin 9 stabs the detonator l6 andthe consequent detonation is transmitted to the booster 13 resulting inthe detonation of the fuse and the explosion of the shell.

If, on the other hand the set back forces induced in the plate 24 ariseout of acceleration of the fuse resulting from an impact or otherextraneous circumstance these accelerations will not be of sufficientmagnitude and/or of sufficient duration for the plate 24 to be fullydisplaced downwardly (as in FIG. 4b) until its upper edge can beretained by the retaining legs which would lead to the arming of thefuse and therefore, when the acceleration induced by these extraneouscircumstances ceases to be effective, the plate is restored to itsoriginal position by the restoring force exerted by the spring 211.

The feature whereby the plate 24 is located in an inclined position withrespect to the adjacent edge of the slider 7 facilitates the readydownward or upward displacement of the plate without excessivefrictional resistance from the slider edge. Thus, after the initialdownward movement of the plate 24 the latter will be somewhat spacedaway from the adjacent edge of the slider 7 and the latter cannottherefore exert any frictional resistance on the movement of the plate24. It will be appreciated that the set back forces effective on theslider 7 effectively lock the slider against the slider housing portion5b and therefore prevent the slider 7 from being pressed against theplate 24, so as to inhibit its motion.

In designing the arming plate, the recess in which it is displaceableand the location of the abutment pins care must be taken to ensure thatlocking of the plate with respect to the pins or with respect to one pinand an adjacent wall of the recess does not take place during thedisplacement of the plate. Thus, if the plate has an excessive freedomfor angular motion a situation can arise whereby the plate abuts bothpins with two respective serrations of opposing slopes and under thesecircumstances the plate will be locked and is therefore incapable offunctioning effectively. In order to avoid such an eventuality it isnecessary to restrict the maximum angle by which the plate can tilt andthis is done by causing the plate to slide in a guideway whosedimensions together with those of the plate limit the angle of tilt ofthe plate by the required amount to prevent locking. The maximum valuewhich this angle can take can be theoretically calculated.

At the same time measures must be taken to ensure that locking does nottake place as a result of the contact between one edge of the plate withthe side wall of the guideway on the one hand and the opposite serratededge of the plate with a pin on the other hand. In order to ensure thisthe design of the plate and the guideway must be so conceived that thevertical distance between the pin and said lowermost edge of the platewhen disposed in contact with the side wall of the guideway exceeds acertain minimum value.

Reference will now be made to FIGS.Sa and 5b of the drawings for atheoretical consideration of the dimensional relationship which must besatisfied so as to avoid locking.

There will first be considered, with reference to FIG. 5a, the problemof locking of the plate between the pins.

As seen in FIG. 5a

7 angle of slope of the plate with respect to the vertical 4: serrationangle B plate width (between serrations) R pin radius h, theoreticalserration depth f spacing between pins Then it can be shown that lockingof this kind can be avoided if the maximum angle of slope 'y is sorestricted that There will now be considered, with reference to FIG. 5bof the drawings the problem of plate locking be tween one pin and theside wall of the guideway. This locking will take place where l which isthe distance from the pin involved to the lower edge of the plate isless than 1 min.

As seen from FIG. 5b

L length of plate B plate width (lower edge) coefficient of frictionangle of friction corresponding to u D Pin diameter 2R then thecondition that locking does not take place is given by In order toensure that both relationships (1) and (2) are satisfied a max value for-y is deductable whereby tan 7 max [b +f- (B B, D)/(2 l min)] In apractical example where f 8.8 mm

L 37 mm 1 min 7.5 mm.

With these values it can be shown that with 7 max 2 3 and l min 2 7mmlocking is avoided.

The particular design of the plate and its guideway has been determinedso as to meet the above referred to theoretical requirements. Thus, inorder to ensure that the angle of tilt does not exceed said maximumvalue whilst at the same time ensuring that the lower edge of the platecannot come into contact with the guideway wall before said minimumdistance is reached the special design of plate and guideway shown inFIG. 2 of the drawings is adopted. Thus, as can be seen the guidewayconsists of an upper wide portion and a lower narrow portion. The upperportion 25 of the plate is widened so that when the plate slides in theguideway it cannot achieve an angle of tilt greater than said maximumallowable value. On the other hand the lower edge of the plate isdisposed in the widened portion of the guideway as long as the distancebetween the pin and the lower edge is less than the minimum value and aslong as the lower edge is located in this widened portion of theguideway contact between the lower edge and the wall of the guidewaycannot take place. By the time, however, that the lower edge of theplate has entered the narrow portion of the guidewaythe distance betweenthe pin and the lower edge exceeds said minimum value and locking cantherefore not occur.

Whilst in the specific embodiment referred to above the abutment systemconsists of a pair of serrated edges of the arming plate and a pair offixed abutment pins other forms of abutment systems can be envisagedwhose function is to ensure that the longitudinal displacement of theplate is accompanied by a transverse displacement thereof. Thus, forexample, the plate can be provided with a longitudinal slot whose inneredges are serrated in a manner similar to the serration of the outeredges of the plate described above, a pin being located within thisslot. Alternatively, the plate can be provided with a pair of outwardlyextending abutment members which are designed to abut respectively apair of serrated edges which is fixed. Thus, in this case the abutmentmembers moved together with the plate whilst the serrated edges remainfixed. In a still further alternative embodiment the serrated edges canbe replaced by fixed abutments such as projecting pins or the like.

Finally, whilst the device in accordance with the invention has beenspecifically described in connection with a set back arming device foruse in a shell fuse other applications of this device can be readilyenvisaged particularly in connection with shell or bomb fuses. Thus, thedevice can be used to provide an indication of the depth to which ashell or bomb penetrates a target (utilizing for this purpose thedisplacement of the plate-like member as a result of the negativeacceleration developed) and for example when the degree of penetrationhas reached a desired level the device can be used to initiate thedetonation of the shell.

We claim:

1. A device for providing an indication of the distance travelled by anobject under conditions of linear acceleration comprising:

a. a housing member adapted to be fixed to the object and having alongitudinal slot elongated in the direction of the acceleration;

b. a plate member; and means mounting the plate member for displacementin the slot in the longitudinal direction and for oscillation in theslot through a limited angle about an axis perpendicular to thelongitudinal direction of the slot;

c. spring means for biasing the plate member in the slot in thelongitudinal direction;

d. cooperable abutment means fixedly mounted on each of the members andlocated at least partially in the longitudinal slot for causing theplate member to oscillate about said axis as the plate member isdisplaced in the slot in the longitudinal direction whereby apredetennined acceleration force acting on the plate member against thebiased action of the spring means for a predetermined period of timedisplaces the plate member through a predetermined distance against thebias of the spring means.

2. A device according to claim 1 wherein the abutment means comprises apair of parallel, spaced, elongated serrated edges formed on one of themembers and a pair of spaced abutments carried by the other member, eachof the abutments being adapted to alternatingly abut the respectiveserrated edges when the plate member is displaced in the slot in thelongitudinal direction.

3. A fuze arming device for a projectile operated by set-back forcesdeveloped during the filing of a projectile comprising:

a. a fuze housing member adapted to be fixed to the projectile andhaving a longitudinal slot elongated in the direction of the set-backforces;

b. a plate member; and means mounting the plate member for displacementin the slot in the longitudinal direction and for oscillation in theslot through a limited angle about an axis perpendicular to thelongitudinal direction of the slot;

0. spring means for biasing the plate member in the slot in thelongitudinal direction against movement in response to the set-backforces;

d. cooperable abutment means fixedly mounted on each of the members andlocated at least partially in the longitudinal slot for causing theplate member to oscillate about said axis as it is displaced in the slotin the longitudinal direction; and

retaining means made efiective when the plate member is displaced in theslot against the spring means through a predetermined distance forretaining the plate member against the bias of the spring means.

4. A fuze arming device according to claim 3 wherein the abutment meanscomprises a pair of spaced, parallel, elongated serrated edges formed onone of the members, and a pair of spaced abutments carried by the othermember, each of the abutments being adapted to altematingly abut therespective serrated edges when the plate member is displaced in the slotin the longitudinal direction.

5. A fuze arming device according to claim 4 including a slider mountedon the housing member for slideable movement in a direction transverseto the direction of displacement of the plate member and into its pathof displacement; and a spring resiliently urging the slider into thepath of displacement of the plate member; the plate member blockingmovement of the slider by the spring until after the plate member isdisplaced through said predetermined distance.

6. A fuze arming device according to claim wherein the dimension of theslot in the direction of slideable movement of the slider is greaterthan the thickness of the plate member for causing the latter to betilted in the slot by the spring acting on the slider as the platemember is displaced through said predetermined distance.

7. A fuze arming device according to claim 6 wherein the plate memberhas a top edge and the retaining means comprises a fixed abutmentpositioned so that the top edge of the plate member can engage behindthe abutment only after the plate member is displaced through saidpredetermined distance and is tilted further by the action of the springbiased slider.

8. A fuze arming device according to claim 7 wherein the plate memberhas a pair of parallel serrated edges, and the pair of abutments arepins carried by the housing member.

1. A device for providing an indication of the distance travelled by anobject under conditions of linear acceleration comprising: a. a housingmember adapted to be fixed to the object and having a longitudinal slotelongated in the direction of the acceleration; b. a plate member; andmeans mounting the plate member for displacement in the slot in thelongitudinal direction and for oscillation in the slot through a limitedangle about an axis perpendicular to the longitudinal direction of theslot; c. spring means for biasing the plate member in the slot in thelongitudinal direction; d. cooperable abutment means fixedly mounted oneach of the members and located at least partially in the longitudinalslot for causing the plate member to oscillate about said axis as theplate member is displaced in the slot in the longitudinal directionwhereby a predetermined acceleration force acting on the plate memberagainst the biased action of the spring means for a predetermined periodof time displaces the plate member through a predetermined distanceagainst the bias of the spring means.
 2. A device according to claim 1wherein the abutment means comprises a pair of parallel, spaced,elongated serrated edges formed on one of the members and a pair ofspaced abutments carried by the other member, each of the abutmentsbeing adapted to alternatingly abut the respective serrated edges whenthe plate member is displaced in the slot in the longitudinal direction.3. A fuze arming device for a projectile operated by set-back forcesdeveloped during the filing of firing projectile comprising: a. a fuzehousing member adapted to be fixed to the projectile and having alongitudinal slot elongated in the direction of the set-back forces; b.a plate member; and means mounting the plate member for displacement inthe slot in the longitudinal direction and for oscillation in the slotthrough a limited angle about an axis perpendicular to the longitudinaldirection of the slot; c. spring means for biasing the plate member inthe slot in the longitudinal direction against movement in response tothe set-back forces; d. cooperable abutment means fixedly mounted oneach of the members and located at least partially in the longitudinalslot for causing the plate member to oscillate about said axis as it isdisplaced in the slot in the longitudinal direction; and e. retainingmeans made effective when the plate member is displaced in the slotagainst the spring means through a predetermined distance for retainingthe plate member against the bias of the spring means.
 4. A fuze armingdevice according to claim 3 wherein the abutment means comprises a pairof spaced, parallel, elongated serrated edges formed on one of themembers, and a pair of spaced abutments carried by the other member,each of the abutments being adapted to alternatingly abut the respectiveserrated edges when the plate member is displaced in the slot in thelongitudinal direction.
 5. A fuze arming device according to claim 4including a slider mounted on the housing member for slideable movementin a direction transverse to the direction of displacement of tHe platemember and into its path of displacement; and a spring resilientlyurging the slider into the path of displacement of the plate member; theplate member blocking movement of the slider by the spring until afterthe plate member is displaced through said predetermined distance.
 6. Afuze arming device according to claim 5 wherein the dimension of theslot in the direction of slideable movement of the slider is greaterthan the thickness of the plate member for causing the latter to betilted in the slot by the spring acting on the slider as the platemember is displaced through said predetermined distance.
 7. A fuzearming device according to claim 6 wherein the plate member has a topedge and the retaining means comprises a fixed abutment positioned sothat the top edge of the plate member can engage behind the abutmentonly after the plate member is displaced through said predetermineddistance and is tilted further by the action of the spring biasedslider.
 8. A fuze arming device according to claim 7 wherein the platemember has a pair of parallel serrated edges, and the pair of abutmentsare pins carried by the housing member.